1. Field of the Invention
This invention relates to axial flow turbine apparatus, and in particular, to a positioning device for locating a thrust bearing with respect to a stationary portion of the turbine.
2. Description of the Prior Art
Rotatably disposed within a casing member of a turbine apparatus is a rotor shaft having mounted thereon a plurality of arrays of rotating blades. The rotating blades are axially interspaced in an alternating configuration with arrays of stationary blading depending from the interior of the casing. As is well known, motive steam is permitted to expand through the alternating arrays of rotating and stationary blades to convert the energy carried by the steam into rotational mechanical energy.
Located at one end of the rotor shaft and mounted in a stationary housing element within the casing is a thrust bearing member. The purpose of the thrust bearing is to act as the anchor point for the rotor and to take any variations in the thrust loading imposed on the rotor so that the desired position thereof can be maintained relative to the stationary blading arrays disposed within the casing. From the anchor point, the rotor is freed to expand axially as the temperatures of the motive steam upon it cause the rotor and the stationary parts to lengthen commensurately.
In erecting the turbine the rotor is installed within the cylinders and all mating surfaces therebetween are set and checked for proper clearances. In order to maintain these clearances, the thrust bearing is positioned on the rotor at the location thereof being designated as the anchor point for the rotor. This position of the thrust bearing with respect to the rotor must be maintained. Thrust bearings of the type used in the turbine art usually have outwardly extending flanges, or support feet, which extend from circumferentially opposite locations on the bearing member. The position of the support feet of the bearing, and therefore the bearing itself, is presently maintained within the bearing housing by an arrangement disposed on each of the oppositely extending support feet. The prior art arrangement includes wedges, liners, and a support cover. The prior art utilizes a complicated and complex fabrication and machining process in order to assure that the bearing member is located in a stationary position relative to the housing.
Once the support foot on each side of the thrust bearing member has been disposed within a corresponding groove provided in the housing so that the thrust bearing is in its required position on the anchor point of the rotor, an axial dimension from the thrust bearing support foot to the housing is obtained. A custom machined shim is installed into position axially intermediate the support foot and the housing on each side of the thrust bearing housing. The shim is held in place by a suitable locating bar secured by screws and lock washers. A support cover is then bolted into place by suitable screws so as to cover the support foot on each side of the bearing housing. A movable wedge disposed on the underside of the support foot is held in place between the underside of the support foot and the side of the groove within the housing while a locating bolt is screwed through the support cover and into the movable wedge. A corresponding wedge surface mounted on the support foot is then positioned next to the movable wedge and by adjusting the two wedges along their engaged surfaces the bearing support foot is located with respect to the axis of the casing. Once the wedges have been aligned any variation between the fixed shim and the axial side of the support foot is recorded so that variations in the shim may be custom machined and the shim redesigned to fit.
Once these preliminary dimensions have been taken and fittings between the corresponding parts made and match-marked, the support cover is removed so that the movable wedge is secured by a bolt and lock washer. The support cover is then replaced into position. The bolt which extends through both the support cover and movable wedge is locked into position through the use of a lock nut and a lock wire.
It is thus apparent that considerable time and effort is expended in both the custom machining and aligning of the various parts of the prior art locating mechanism and in the extensive operations which are required in order to accurately position the bearing member relative to the stationary housing element. It is apparent from the discussion of the prior art arrangement above, that parts must be match-marked to insure that the elements will always be assembled in the same location should the unit ever be disassembled. This of course necessitates extra expense in both labor and down time during reassembly. It is also noted that for the support location of each support foot, which extends from each side of the bearing member, the alignments of part and labor described above must occur twice.
It is evident that a more efficient and expeditious process of mounting the thrust bearing with respect to a stationary element within the casing and a more effective device for positioning the thrust bearing relative to the casing is necessary.